offseting DATA_ADDR

[Matt Thomas]

[I've wondered about this for years and I'm finally going to ask it.]

Why isn't DATA_ADDR/SHLIB_DATA_ADDR defined by default to start on a  
segment boundary?
Why is it defined to start at about the same offset as where text ends  
by default?

For example, a MIPS N32 shared library has the following load sections  
by default:

Program Headers:
   Type           Offset   VirtAddr   PhysAddr   FileSiz MemSiz  Flg  
Align
   LOAD           0x000000 0x00000000 0x00000000 0xfc140 0xfc140 R E  
0x10000
   LOAD           0x0fc140 0x001fc140 0x001fc140 0x071c0 0x17300 RW   
0x10000

If I change DATA_ADDR/SHLIB_DATA_ADDR to be defined as ALIGN($ 
{SEGMENT_SIZE}), I get:

Program Headers:
   Type           Offset   VirtAddr   PhysAddr   FileSiz MemSiz  Flg  
Align
   LOAD           0x000000 0x00000000 0x00000000 0xfc140 0xfc140 R E  
0x10000
   LOAD           0x100000 0x00100000 0x00100000 0x071c0 0x17300 RW   
0x10000

That seems to me to be a much more sane layout.  What does the extra  
0xfc140 offset buy me?  There is a cost overhead to that wasted space  
(unused PTEs in the kernel, can't easily use large page sizes  
for .data).

I can see that it might be used in a small set of cases (ROM images  
copied to ram) but in the vast majority of normal usage it seems to  
just waste address space.

Can anyone enlighten me?